BACKGROUND

The present invention relates, in general, to motors and, more particularly, to three phase motors.

Multi-phase motors are used in a variety of applications including disc drives, digital video disc players, scanners, printers, plotters, actuators used in automotive and aviation industries, etc. Generally, multiple phase motors include a stationary portion or stator that produces a rotating magnetic field and a non-stationary portion or rotor in which torque is created by the rotating magnetic field. The torque causes the rotor to rotate which in turn causes a shaft connected to the rotor to rotate. The motors are driven by motor drive circuits.

Motor drive circuits are designed to meet desired motor performance parameters which may include noise level specifications, start-up specifications, maximum rotational speed specifications, etc. Noise specifications may be set to provide continuity of current flow during motor startup, or during motor rotation, or during motor stoppage. Start-up or motive power specifications may be set so that the motor reliably starts. Rotational speed specifications may be set to ensure there is sufficient torque drive to cover a large number of different motors. For example, the desired rotational speed of a server is higher than that of a personal computer. It is commonly believed that three-phase motors are better at achieving the desired specifications compared to single phase motors; however, three-phase motors cost more than single phase motors. In addition, three-phase motors provide current having sinusoidal characteristics from motor start-up to motor stoppage or cessation and they allow accurate determination of motor position and rotation speed. Three-phase motors typically include three Hall sensors, which is one of the reasons these motors are more expensive to manufacture. A Hall sensor may be referred to as a Hall element. U.S. Pat. No. 6,359,406 issued to Hsien-Lin Chiu et al. on Mar. 19, 2002, discloses three-phase motors and in particular discloses a three-phase motor having two Hall sensors or two Hall elements. A drawback with this technology is that it uses special bias circuitry that complicates its design and increases costs. A technique to lower the cost of three-phase motors is to manufacture the motor drive circuitry as a sensorless motor drive circuit, i.e., a motor without sensors. U.S. Pat. No. 6,483,279 issued to Shinichi Miyazaki et al. on Nov. 19, 2002, discloses a three-phase motor without sensors. A drawback with sensor-less motor drive configurations is that they may fail to start if the inductive voltage of the coil is small.

Accordingly, it would be advantageous to have a multi-phase motor drive circuit and a method for driving the motor that is not overly complex and that can handle small inductive coil voltages. It is desirable for the multi-phase drive circuit and method to be cost and time efficient to implement.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures, in which like reference characters designate like elements and in which:

FIG. 1 is a diagrammatic representation of a motor that is driven by a drive circuit in accordance with an embodiment of the present invention;

FIG. 2 is a block diagram further illustrating the drive circuit of FIG. 1;

FIG. 3 is a flow diagram of starting a motor in accordance with another embodiment of the present invention;

FIG. 4A is a diagrammatic representation of the motor of FIG. 1 stopped in a first position;

FIG. 4B is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 4C is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 4D is a diagrammatic representation of the motor of FIG. 1 stopped in a first position;

FIG. 4E is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 4F is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 4G is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 5A is a diagrammatic representation of the motor of FIG. 1 stopped in a first position;

FIG. 5B is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 5C is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 5D is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 5E is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 5F is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 5G is a diagrammatic representation of the motor of FIG. 1 stopped in another position;

FIG. 6 is a flow diagram of starting a motor in accordance with another embodiment of the present invention;

FIG. 7 illustrates the application of the control torque in moving a rotor in accordance with a duty adjustment embodiment;

FIG. 8 is a diagrammatic representation of starting the motor of FIG. 1 in accordance with an embodiment of the present invention;

FIG. 9 is a flow diagram for calculating the duty levels in accordance with another embodiment of the present invention;

FIG. 10 is a startup procedure in accordance with another embodiment of the present invention;

FIG. 11 is a block diagram of a control circuit configured for starting a motor in accordance with another embodiment of the present invention;

FIG. 12 is a flow diagram for a starting motor in accordance with another embodiment of the present invention; and

FIG. 13 is a graph of input duty and output duty in accordance with another embodiment of the present invention.

For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or an anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain n-channel or p-channel devices, or certain n-type or p-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action and the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten per cent (10%) (and up to twenty per cent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of exactly as described.

It should be noted that a logic zero voltage level (V_L) is also referred to as a logic low voltage or logic low voltage level and that the voltage level of a logic zero voltage is a function of the power supply voltage and the type of logic family. For example, in a Complementary Metal Oxide Semiconductor (CMOS) logic family a logic zero voltage may be thirty percent of the power supply voltage level. In a five volt Transistor-Transistor Logic (TTL) system a logic zero voltage level may be about 0.8 volts, whereas for a five volt CMOS system, the logic zero voltage level may be about 1.5 volts. A logic one voltage level (V_H) is also referred to as a logic high voltage level, a logic high voltage, or a logic one voltage and, like the logic zero voltage level, the logic high voltage level also may be a function of the power supply and the type of logic family. For example, in a CMOS system a logic one voltage may be about seventy percent of the power supply voltage level. In a five volt TTL system a logic one voltage may be about 2.4 volts, whereas for a five volt CMOS system, the logic one voltage may be about 3.5 volts.

DETAILED DESCRIPTION

FIG. 1 is a diagrammatic representation of a three-phase motor 10 that is driven by a drive circuit 12 in response to one or more signals from a Hall sensor 14 in accordance with an embodiment of the present invention. Drive circuit 12 may be referred to as a driver and Hall sensor 14 may be referred to as a Hall element. Three-phase motor 10 includes a stator 16 and a rotor 18 having a portion 20 magnetized with a first pole and a portion 22 magnetized with a second pole. By way of example, portion 20 is a north pole and portion 22 is a south pole. A coil 24 is coupled to or mounted on a portion of stator 16, a coil 26 is coupled to or mounted on another portion of stator 16, and a coil 28 is coupled to or mounted on yet another portion of stator 16. Drive circuit 12 is coupled to Hall sensor 14 via an electrical interconnect 29, to coil 24 via an electrical interconnect 30, to coil 26 via an electrical interconnect 32, and to coil 28 through an electrical interconnect 32. Coil 24 may be referred to as a U-phase winding, coil 26 may be referred to as a W-phase winding, and coil 28 may be referred to as a V-phase winding. Electrical interconnects 30, 32, and 34 may be wires, electrically conductive traces, or the like.

FIG. 2 is a block diagram 50 further illustrating drive circuit 12. It should be noted that block diagram 50 includes diagrammatic representations of drive circuit 12, three-phase motor 10, and Hall sensor 14. Drive circuit 12 includes an FG signal masking circuit 52, a rotational state generation circuit 54, a pulse width modulation (â€œPWMâ€ ) detection circuit 56, a timer 58, a status controller 60, a duty control controller 62, an output duty generation circuit 64, a drive control signal generation circuit 66, and an output drive stage 68. More particularly, FG signal masking circuit 52 may be comprised of an FG signal edge detector 70, a counter 72, and an FG signal judgment circuit 74. FG signal edge detector 70 has an input that serves as an input 76 of drive circuit 12, an output connected to an input of counter 72 and an output connected to an input of FG signal judgment circuit 74. An output 78 of FG signal judgment circuit 74 serves as an output of FG signal masking circuit 52. FG signal masking circuit 52 may be referred to as a chattering mitigation circuit or a chattering mitigation feature.

Rotational state generation circuit 54 has inputs 80 and 82, an input/output 84, and may be referred to as an FG generation circuit. Output 78 of FG signal masking circuit 52 is connected to input 80 of FG generation circuit 54. Input/output 84 may be referred to as an input/output node, an I/O node, an input/output terminal, an I/O terminal, or the like. Rotational state generation circuit 54 may be comprised of a control circuit 86 coupled to a multiplier circuit 88. It should be noted that input 80 and input 84 are connected to multiplier control circuit 86 and input/output 84 is connected to multiplier circuit 88. PWM detection circuit 56 has an output connected to an input of state controller 60 and to an input of duty control controller 62 and is configured to determine the speed of rotor 18. It should be noted that if the duty range is small the speed of the rotor is smaller than if the duty range is large. Timer 58 has an output connected to input 82 of rotational state generation circuit 54 and to an input 92 of state controller 60 and may include a timer counter 90. In addition, state controller 60 has an input/output 94 connected to an input/output 84 of rotational state generation circuit 54, an input 98 connected to output 78 of FG signal masking circuit 52, and an input/output 96 connected to an input/output 100 of duty control controller 62. By way of example, duty control controller 62 is comprised of a calculation device 102 configured to determine an amount of change to the duty cycle, a summer 104, and a PWM converter 106. Calculation device 102 has an input that serves as input/output 100 and an output connected to an input of summer 104. In addition, summer 104 has an output that is connected to an input of PWM output converter 106 and to another input of summer 104. An output 108 of PWM output converter 106 serves as an output of duty control controller 62. State controller 60 is configured for determining the status or condition of the FG signal and the PWM signal and duty control controller 62 is configured to control an output sine wave, which helps to make the motor quieter.

Output duty generation circuit 64 has an input 110 connected to an output 99 of output of state controller 60, an input 112 connected to output 108 of output duty generation circuit 62, and a plurality of outputs 114, 116, and 118 connected to corresponding inputs of drive control signal generation circuit 66, which signal generation circuit 66 has a plurality of outputs 120, 122, and 124 connected to corresponding inputs of output drive stage 68. In accordance with an embodiment, drive stage 68 includes driver devices 126, 128, and 130 having inputs that serve as inputs 126A, 128A, and 130A of output drive stage 68, a pair 66A of transistors having a terminal connected to U-phase winding 24, a pair 66B of transistors having a terminal connected to W-phase winding 26, and a pair 66C of transistors having a terminal connected to V-phase winding 28. Pair of transistors 66A is comprised of transistors 66A₁and 66A₂, wherein each transistor has a control electrode, and a pair of current carrying electrodes. The control electrodes of transistors 66A₁and 66A₂are coupled for receiving control signals from driver device 126, one current carrying electrode of transistor 66A₁is coupled for receiving a source of potential V_DDand the other current carrying electrode of transistor 66A₁is connected to a current carrying electrode of transistor 66A₂. The other current carrying terminal of transistor 66A₂is coupled for receiving a source of potential V_SSsuch as, for example, a ground potential. The commonly connected current carrying electrodes of transistors 66A₁and 66A₂are connected to U-phase winding 24.

Pair of transistors 66B is comprised of transistors 66B₁and 66B₂, wherein each transistor has a control electrode, and a pair of current carrying electrodes. The control electrodes of transistors 66B₁and 66B₂are coupled for receiving control signals from driver device 128, one current carrying electrode of transistor 66B₁is coupled for receiving a source of potential V_DDand the other current carrying electrode of transistor 66B₁is connected to a current carrying electrode of transistor 66B₂. The other current carrying terminal of transistor 66B₂is coupled for receiving a source of operating potential V_SSsuch as, for example, a ground potential. The commonly connected current carrying electrodes of transistors 66B₁and 66B₂are connected to U-phase winding 26.

Pair of transistors 66C is comprised of transistors 66C₁and 66C₂, wherein each transistor has a control electrode, and a pair of current carrying electrodes. The control electrodes of transistors 66C₁and 66C₂are coupled for receiving control signals from driver device 130, one current carrying electrode of transistor 66C₁is coupled for receiving a source of potential V_DDand the other current carrying electrode of transistor 66C₁is connected to a current carrying electrode of transistor 66C₂. The other current carrying terminal of transistor 66C₂is coupled for receiving a source of operating potential V_SSsuch as, for example, a ground potential. The commonly connected current carrying electrodes of transistors 66C₁and 66C₂are connected to U-phase winding 28.

A comparator 136 has inputs connected to corresponding inputs of a Hall sensor 14 and an output 138 connected to input 76 of rotational state generation circuit 54.

It should be noted that in accordance with an alternative embodiment, FG signal masking circuit 52 is absent from drive circuit 12 and that output 138 of comparator 136 is commonly connected to input 76 of rotational state generation circuit 54 and to input 98 of state controller 60.

Starting a three-phase motor such as, for example, three-phase motor 10 using a Hall sensor 14 in accordance with an embodiment of the present invention is described with reference to flow diagram 150 shown in FIG. 3, FIGS. 4A-4G, FIGS. 5A-5G, and flow diagram 180 shown in FIG. 9. Referring now to flow diagram 150, at a time indicated by box 152, the process for staring three-phase motor 10 begins, wherein drive circuit 12 may be stopped, beginning to stop, or nominally rotating. At decision diamond 154, drive circuit 12 confirms whether rotor 18 has stopped rotating. If rotor 18 is rotating or moving, i.e., rotor 18 has not stopped, drive circuit 12 and continues monitoring the rotational status of rotor 18 as indicated by the No or N of decision diamond 154. If rotor 18 has stopped rotating, drive circuit 12 determines the north-south magnetic orientation of Hall sensor 14 as indicated by decision diamond 156, and, in accordance with embodiments of the present invention, moves rotor 18 in a clockwise direction or a counterclockwise direction so that the north pole of rotor 18 or the south pole of rotor 18 are adjacent to or aligned with Hall sensor 14 as indicated by boxes 158 and 160.

The north pole (â€œNâ€ ) and the south pole (â€œSâ€ ) of rotor 18 may stop in a plurality positions relative to Hall sensor 14. For example, FIGS. 4A-4G are diagrammatic representations of three-phase motor 10 that includes U-phase winding 24, W-phase winding 26, and V-phase winding 28 described with reference to FIG. 1 showing rotor 18 stopped at different locations or positions. It should be noted that in FIGS. 4A-4G, U-phase winding 24 and W-phase winding 26 are magnetized with a south polarity and V-phase winding 28 is magnetized with a north polarity. In FIG. 4A the north pole of rotor 18 has stopped near or adjacent to U-phase winding 24 and the south pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 so that rotor 18 is in a position P₁. In FIG. 4B, the north pole of rotor 18 has stopped near or adjacent to Hall sensor 14 and the south pole of rotor 18 has stopped near or adjacent to V-phase winding 28 so that rotor 18 is in a position P₂. In FIG. 4C the north pole of rotor 18 has stopped near or adjacent to W-phase winding 26 and the south pole of rotor 18 has stopped between V-phase winding 28 and U-phase winding 24 so that rotor 18 is in a position P₃. In FIG. 4D the north pole of rotor 18 has stopped between U-phase winding 24 and Hall sensor 24 and the south pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 so that rotor 18 is in a position P₄. In FIG. 4E the north pole of rotor 18 has stopped between Hall sensor 24 and W-phase winding 26 and the south pole of rotor 18 has stopped between V-phase winding 28 and U-phase winding 24 so that rotor 18 is in a position P₅. In FIG. 4F the north pole of rotor 18 has stopped between U-phase winding 24 and V-phase winding 28 and the south pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 so that rotor 18 is in a position P₆. In FIG. 4G the north pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 and the south pole of rotor 18 has stopped between V-phase winding 28 and U-phase winding 24 so that rotor 18 is in a position P₇. In FIG. 4H the north pole of rotor 18 has stopped near or adjacent to V-phase winding 28 and the south pole of rotor 18 has stopped near or adjacent to Hall sensor 24 so that rotor 18 is in a position P₈.

In FIGS. 5A-5G, U-phase winding 24 and W-phase winding 26 are magnetized with a north polarity and V-phase winding 28 is magnetized with a south polarity. In FIG. 5A, the south pole of rotor 18 has stopped near U-phase winding 24 and the north pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 so that rotor 18 is in a position P_1A. In FIG. 5B, the south pole of rotor 16 has stopped near or adjacent to Hall sensor 14 and the north pole of rotor 18 has stopped near or adjacent to V-phase winding 28 so that rotor 18 is in a position P_2A. In FIG. 5C the south pole of rotor 18 has stopped near or adjacent to W-phase winding 26 and the north pole of rotor 18 is between V-phase winding 28 and U-phase winding 24 so that rotor 18 is in a position P_3A. In FIG. 5D the south pole of rotor 18 has stopped between U-phase winding 24 and Hall sensor 24 and the north pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 so that rotor 18 is in a position P_4A. In FIG. 5E the south pole of rotor 18 has stopped between Hall sensor 24 and W-phase winding 26 and the north pole of rotor 18 has stopped between V-phase winding 28 and U-phase winding 24 so that rotor 18 is in a position P_5A. In FIG. 5F the south pole of rotor 18 has stopped between U-phase winding 24 and V-phase winding 28 and the north pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 so that rotor 18 is in a position P_6A. In FIG. 5G the south pole of rotor 18 has stopped between V-phase winding 28 and W-phase winding 26 and the north pole of rotor 18 has stopped between V-phase winding 28 and U-phase winding 24 so that rotor 18 is in a position P_7A. In FIG. 5H the south pole of rotor 18 has stopped near or adjacent to V-phase winding 28 and the north pole of rotor 18 has stopped near or adjacent to Hall sensor 24 so that rotor 18 is in a position P_8A.

In operation and in response to rotor 18 stopping such that its north pole stator is not adjacent to Hall sensor 14 as shown in FIGS. 4A and 4C-4G, drive circuit 12 generates control signals to rotate rotor 18 in a clockwise direction or a counter clockwise direction so that the north pole of rotor 18 is adjacent Hall sensor 14 as shown in FIG. 4B. Alternatively, in response to rotor 18 stopping such that its south pole is not adjacent to Hall sensor 14 as shown in FIGS. 5A and 5C-5G, drive circuit 12 generates control signals to rotate the rotor 18 in a clockwise direction or a counterclockwise direction so that the south pole of the rotor 18 is adjacent Hall sensor 14 as shown in FIG. 5B. Rotor 18 is moved in accordance with the magnetic force sensed by Hall sensor 14. By way of example, rotor 18 may be positioned in response to Hall sensor 14 sensing a maximum magnetic force from the north pole or a maximum magnetic force from the south pole. Alternatively, rotor 18 may be positioned in response to Hall sensor 14 sensing a magnetic force from the north pole being greater than a north reference force (MF_N) or the rotor may be positioned in response to Hall sensor 14 sensing a magnetic force from the south pole being greater than a south reference force (MF_S), where north reference force MF_Nmay be equal to south reference force MF_S. Motor 10 may be started in response to rotor 18 being positioned in the primary position or the secondary position. Thus, drive circuit 12 performs north side retreat processing to move the north pole of rotor 18 to be adjacent to Hall sensor 14 as indicated by box 158 or drive circuit 12 performs south side retreat processing to move the south pole of rotor 18 to be adjacent to Hall sensor 14 as indicated by box 160.

FIG. 6 is a diagrammatic representation illustrating that when rotor 18 is positioned at position P₁or position P₃as shown in FIGS. 4A and 4C, respectively, a barrier 19 must be overcome for rotor 18 to arrive at position P₂, i.e., a predetermined or desired position that helps to reliably start motor 10 by applying a positive torque to rotor 18, shown in FIG. 4B. In addition, FIG. 6 illustrates that when rotor 18 is positioned at position P_1Aor position P_3Aas shown in FIGS. 5A and 5C, respectively, barrier 19 must be overcome for rotor 18 to arrive at position P_2A, i.e., a predetermined or desired position, shown in FIG. 5B. Barrier 19 represents issues such as ringing, the time needed to stop at a fixed position when the rotor has stopped at a distance away from the desired starting position, etc.

FIG. 7 illustrates the application of the control torque in moving rotor 18 from the position shown in, for example, FIG. 5A to the position shown in FIG. 5B, i.e., the primary configuration in accordance with a duty adjustment embodiment. From time t₀to time t₁, drive circuit 12 applies a drive signal U_DRto U-phase winding 24 having a duty cycle that exceeds the duty cycle of the cogging torque and a drive signal W_DRto W-phase winding 26 having a duty cycle that exceeds the duty cycle of the cogging torque. By way of example, the duty cycles of drive signals U_DRand W_DRare gradually increased from 0 to 50 percent (%). At time t₁, the duty cycles of drive signals U_DRand W_DRare at 50%, which exceeds the duty cycle of the cogging torque. The time from about t₀to about t₁may be referred to as mode 1. In response to reaching the duty cycle that exceeds that of the cogging torque at time t₁, drive circuit 12 generates drive signals that reduce the duty cycles of drive signals U_DRand W_DRto reduce the ringing of the rotor, i.e., to reduce the oscillations of the rotor about a rotor stopping location. By way of example, drive circuit 12 reduces the duty cycles of drive signals U_DRand W_DRto 25%. The time from about t₁to about t₃may be referred to as mode 2. At time t₃, drive circuit 12 increases the duty cycles of drive signals U_DRand W_DRuntil rotor 18 begins to move or rotate, wherein rotor 18 begins to rotate in response to the drive signals U_DRand W_DRhaving a duty cycle of 50%, thus drive circuit 12 increases the duty cycles of drive signals U_DRand W_DRto 50% at time t₄. In response to rotor 18 reaching the desired position, e.g., rotor 18 being in the first configuration or the second configuration, at time t₅, drive circuit 12 generates a drive signal U_DRhaving a duty cycle of 50% and a drive signal W_DRhaving a duty cycle that decreases, which causes rotor 18 to stop rotating at the desired position. The time from about t₃to about t₅may be referred to as mode 3. At time t₆, drive circuit 12 generates a drive signal V_DRthat increases from, for example 0 to 50% and generates drive signals U_DRand W_DRhaving duty cycles of 50% and 0, respectively. The time from about t₅to about t₆may be referred to as mode 4. The time from about t₆to about t₇may be referred to as mode 5. At time t₇, rotor 18 has begun to rotate motor 10 enters a seventh operating mode, i.e., mode 7, at about time T₇and drive signals U_DR, W_DR, and V_DRbecome sine waves having different phases from each other. Thus, the duty of the drive signal, i.e., the UVW drive signals, is gradually increased until a predetermined duty is achieved and the duty is lowered.

FIG. 8 illustrates moving rotor 18 in accordance with an embodiment of the present invention. FIG. 8 illustrates rotating or moving rotor 18 so that it is positioned in the secondary configuration in preparation for starting motor 10. Rotor 18 may be in position P_1Aor P_3Aas shown in FIG. 5A and FIG. 5C, respectively, and shown in FIG. 8. As discussed with reference to FIG. 5, motor 10 moves rotor 18 to be in position P_1Bas shown in FIG. 5B. FIG. 8 illustrates that drive circuit 12 generates drive signals that change the polarity of the magnetic field at W-phase winding 26 from north to south, causing rotor 18 to rotate in a clockwise direction to position P_2A1. In response to moving to position P_2A1, drive circuit 12 generates drive signals that change the polarity of the magnetic field at V-phase winding 28 from south to north so that rotor 18 continues rotating in the clockwise direction to position P_2A2. In response to moving to position P_2A2, drive circuit 12 generates drive signals that change the polarity of the magnetic field at U-phase winding 24 from north to south so that rotor 18 continues rotating in the clockwise direction to position P_2A3. In response to moving to position P_2A3, drive circuit 12 generates drive signals that change the polarity of the magnetic field at W-phase winding 26 from south to north so that rotor 18 continues rotating in the clockwise direction to position P_2A4. The rotation of rotor 18 continues until the desired stop position or location is achieved.

Referring again to FIG. 3, at box 162, drive circuit 12 generates a control signal to start three-phase motor 10. In response to starting three-phase motor 10 an FG signal is generated and drive circuit 12 detects an edge of the FG signal, i.e., a rising edge or a falling edge of the FG signal. If an edge of an FG signal has not been detected, drive circuit 12 initiates control procedures for the motor being in a locked condition or a stuck condition as indicated by decision diamond 164 and box 166. Thus, in response to not detecting a rising edge or a falling edge of an FG signal at decision diamond 164, control circuit 12 implements or begins a locked processing procedure.

If an edge of the FG signal has been detected, control circuit 12 begins a motor start procedure as indicated by decision diamond 164 and box 168. Thus, in response to detecting a rising edge or a falling edge of the FG signal at decision diamond 164, control circuit 12 implements or begins a drive start processing procedure that includes generating a sine wave drive signal. Accordingly, three-phase motor 10 is ready to start as indicated by box 170.

FIG. 9 is a flowchart 180 of a process from the beginning of moving rotor 18 to an initial position to the completion of the initial process. Each mode is controlled by a timer. Motor 10 shifts to another mode in response to reaching a pre-determined time. At box 182, the retreat movement or the start of the first action movement commences. At decision diamond 184, drive circuit 12 determines whether a predetermined time has elapsed in response to drive circuit 12 entering an operating mode. If the time has elapsed, indicated by a Yes at decision diamond 184, drive circuit 12 shifts to the next mode indicated by box 186 and then continues with addition or subtraction processing to generate a signal for moving rotor 18 indicated by box 188. If the time has not elapsed, indicated by a No at decision diamond 184, drive circuit 12 continues with addition or subtraction processing to generate a signal for moving rotor 18, without shifting modes indicated by box 188. After processing in box 188, the presence of an edge is detected as indicated by decision diamond 190. If an FG edge signal is detected, identified by the No branch of decision diamond 190, locked processing begins as indicated by box 191. If an FG edge signal is detected, indicated by the Yes branch of decision diamond 190, movement of rotor 18 to an initial position and initial process are completed in response to detecting the FG signal during mode 4 or mode 6 (indicated by box 192), and it transitions to sine-wave-drive signal, i.e., a drive signal having a sinusoidal configuration.

In accordance with another embodiment, at an early stage of the initiation control procedure a masking phase is started as illustrated by timing diagram 200 shown in FIG. 10. At time t₀, the FG signal, V_FG, transitions from level V_Lto level V_Hin response to detecting an edge of an initial rise of the FG signal and the output signal of comparator 136 transitions from voltage level V₁to voltage level V₂. An edge detector indicates that a rising edge of the FG signal occurs at about time t₀. In addition, a mask signal V_Mtransitions from voltage level V₃to voltage level V₄and the output of counter 90 increases in response to counter 90 beginning to count.

At time t₁, the output signal of comparator 136 transitions from voltage level V₂to voltage level V₁and an edge detector indicates that a falling edge of the FG signal occurs at about time t₁. It should be noted that mask signal V_Mremains at voltage level V₄at time t₁because counter 90 has not reached a predetermined count value.

At time t₂, the output signal of comparator 136 transitions from voltage level V₁to voltage level V₂and the edge detector indicates that a rising edge of the FG signal occurs at about time t₂. It should be noted that mask signal V_Mremains at voltage level V₄at time t₂because counter 90 has not reached a predetermined count value.

At time t₃, counter 90 reaches a predetermined count value and mask signal VM transitions from voltage level V₄to voltage level V₃, thereby unmasking the FG signal V_FGso that control circuit can respond to FG signal V_FG.

At time t₄, the output signal of comparator 136 transitions from voltage level V₂to voltage level V₁and an edge detector indicates that a falling edge of the FG signal occurs at about time t₄. In addition, mask signal V_Mtransitions from voltage level V₃to voltage level V₄and the output of counter 90 increases in response to counter 90 beginning to count.

In accordance with another embodiment of the present invention, a motor such as, for example, motor 10 is started with a positive torque by gradually increasing the duty of the input PWM signal until the duty of the PWM signal reaches a minimum start duty at which rotor 18 of motor 10 begins to rotate. Rotation of rotor 18 can be referred to as movement of rotor 18 or turning of rotor 18. Then the duty is gradually decreased.

FIG. 11 is a block diagram of a control circuit 250 configured for starting motor 10 that rotor 18 rotates in response to gradually increasing the duty of a PWM signal. Control circuit 250 is comprised of a PWM counter 252, an input duty calculation device 254, a calculation device 256, a summer 258, state controller 60, and an output generation circuit 260. More particularly, PWM counter 252 has an input 252A coupled for receiving a PWM signal and outputs 252B and 252C, where output 252B is connected to an input 254A of input duty calculation device 254 and output 252C is connected to an input 254B of input duty calculation device 254. An output 254C of input duty calculation device 254 is connected to an input 256A of calculation device 256. Summer 258 has an input connected to an output 256B and an input connected to its output in a feedback configuration. The output of summer 258 is also connected to an input 60A of state controller 60 and to an input 260A of output generation circuit 260. State controller 60 has outputs 60B and 60C connected to inputs 256C and 256D of calculation device 256, respectively. In addition, state controller 60 has an input 60D coupled for receiving a control signal.

FIG. 12 is a flow diagram 270 for starting motor 10 in accordance with another embodiment of the present invention. At a beginning step identified by box 272 start processing begins by determining if the input duty of the PWM signal is less than a start guarantee duty of motor 10 as indicated by decision diamond 274. In response to the input duty level being less than the start guarantee value, i.e., the YES branch of decision diamond 274, circuit 250 increases the duty of the FG signal as indicated by box 276. Circuit 250 then determines whether the duty has increased to the start guarantee level at decision diamond 278. In response to the duty not being at the start guarantee level, circuit 250 continues to increase the duty of the FG signal as indicated by the NO branch of decision diamond 278. In response to the duty being at or above the start guarantee level, circuit 250 gradually decreases the duty of the FG signal as indicated by the YES branch of decision diamond 278 and box 280. Circuit 250 monitors the duty of the FG signal to determine if the duty has reached a predetermined level as indicated by decision diamond 282. More particularly, if the predetermined duty level has not been reached, circuit 250 continues decreasing or reducing the duty of the FG signal as indicated by the NO branch of decision diamond 282. If the duty level has reached the predetermined level, the start up process is terminated and the motor continues to run as indicated by the YES branch of decision diamond 282 and box 290.

Referring again to decision diamond 274, if the input duty level is greater than the start guarantee level, i.e., the NO branch of decision diamond 284, circuit 250 increases the duty of the FG signal as indicated by box 284. Circuit 250 monitors the duty of the FG signal to determine if the duty has reached a predetermined level as indicated by decision diamond 286. More particularly, if the predetermined duty level has not been reached, circuit 250 continues increasing the duty of the FG signal as indicated by the NO branch of decision diamond 282. If the duty level has reached the predetermined level, the start up process is terminated and the motor continues to run as indicated by the YES branch of decision diamond 286 and box 290.

By way of example, FIG. 13 indicates that for the predetermined output duty, i.e., the duty of the FG signal, being 30%, the input duty, i.e., the duty of the input PWM signal, being 10%, and the predetermined duty level of the FG signal being 30%, the duty of the FG signal is increased from 20% until it reaches the predetermined value of 30%, then the duty is gradually reduced until motor 10 starts.

Thus, a signal indicating an increase or decrease between duty value of the input PWM signal and information of guaranteeing start-up value and existing output duty value of the FG signal is sent state controller 60. Once state controller 60 receives the information, state controller 60 determines whether to increase or decrease the duty of the output FG signal, the amount of the increase or decrease, and the timing of increase or decrease. Quantity of addition calculation device 256 controls next output PWM duty width based on the information received from state controller 60.

Although specific embodiments have been disclosed herein, it is not intended that the invention be limited to the disclosed embodiments. Those skilled in the art will recognize that modifications and variations can be made without departing from the spirit of the invention. It is intended that the invention encompass all such modifications and variations as fall within the scope of the appended claims.